The next 10 days will be some of the most important in Juergen Klinsmann's dual tenure as coach of the men's national team and technical director for U.S. Soccer.

Sunday morning he'll reveal his roster for home and away World Cup qualifiers with Guatemala on Friday and March 29. On Saturday Andi Herzog, his chief assistant, revealed the roster he and Klinsmann have chosen for two Olympic qualifiers with Colombia, to be played on the same dates.

Four games, three countries, two teams. And very little room for error.

Klinsmann is nearly five years into his mission to build the U.S. into a world power in soccer and his progress has stalled. Although the U.S. opened the year with victories over Iceland and Canada, those wins were only the 12th and 13th in 27 games since the 2014 World Cup. Included in those results was a three-game losing streak at home last fall, the first time that has happened since 1997; the earliest exit from a CONCACAF Gold Cup since 2003 last summer; and a loss to Mexico in a Confederations Cup playoff in October.

Klinsmann can ill afford another slip-up against Guatemala in the six-game semifinal round of World Cup qualifying. After beating St. Vincent and the Grenadines and playing Trinidad and Tobago to a draw in November, the U.S. leads its four-team group and can advance to the next round simply by finishing in the top two.

World Cup qualifiers are never easy, especially on the road, where the U.S. will play Friday. But given the opponent, a country that hasn't beaten the U.S. in nearly three decades, anything less than a win and a draw in the two games would be a failure.

The stakes are just as high for the U-23 team against Colombia.

When the U.S. failed to qualify for the last Olympics, Klinsmann said he would "make sure … that doesn't happen again." Yet Herzog, who coaches the team, failed to fulfill that promise when the U.S. finished third in last fall's CONCACAF tournament, forcing it into a last-ditch playoff for the final berth in this summer's Games in Brazil.

"The perfect result is we win these two games against Colombia and then we go to Rio," Herzog said Saturday.

But that's not the end of the challenges for Klinsmann. Looming on the horizon is June's prestigious Copa America — where the U.S. was drawn into a difficult group alongside Costa Rica, Colombia and Paraguay — and as many as four more World Cup qualifiers in the fall. That's a lot to tackle at one time.

Plus he's also having to deal with remaking a senior team that has suddenly grown old. Of the 11 players who started in the last World Cup match in Brazil, only defender Omar Gonzalez will be younger than 30 when the next World Cup kicks off in two years.

As a result many of them will be watching the games from Russia on television.

"It's a fascinating topic always between two World Cup cycles: Which younger players will take over from the older players?" Klinsmann said. "This will continue the next two years in the World Cup qualifiers … but it will also continue through Copa America.

"There's a lot of competition going on in our squad."

Which brings us back to the next 10 days.

In setting rosters for the two teams Klinsmann gave precedence to the World Cup qualifiers. Defenders John Brooks and DeAndre Yedlin, who are both age-eligible for the U-23 team, were selected for the senior team, for example, while forward Jordan Morris will play against Colombia.

"Priority is World Cup qualifying, so there are no compromises" Klinsmann said.

However roster changes can be made between games. So if the senior team wins its opener in Guatemala on Friday and the U-23 loses in Colombia, it's not inconceivable that Klinsmann could send Herzog some reinforcements for the second game of Olympic qualifying in Frisco, Texas.

The senior team will play its second game in Columbus, Ohio, where it has never lost, while the U-23 roster has been riddled by injuries with Tottenham Hotspur defender Cameron Carter-Vickers, Rangers midfielder Gedion Zelalem and Utrecht forward Rubio Rubin among those who are unavailable.

In the meantime, the Guatemala games figure to give Klinsmann a clear look at some of the problems facing his team, beginning at goalkeeper. Veterans Tim Howard, 37, and Brad Guzan, 31, are expected to be selected Sunday despite the fact Howard has lost his starting job at Everton and Guzan has played only five Premier League games this year for relegation-bound Aston Villa.

Up front, Toronto's Jozy Altidore is once again battling hamstring problems although he probably will be called up despite the fact he sat out the first two weeks of the Major League Soccer season. Seattle's Clint Dempsey, 33, passed over in for last four national team games, is also likely to be summoned along with the Galaxy's Gyasi Zardes and Bobby Wood, who is having a great season for Union Berlin in Germany's second division.